1. Technical Field
The present invention relates to a media conveyance control method that can suppress variation in the tension on a continuous medium delivered and conveyed from a roll, and to a printer.
2. Related Art
A printer that prints on continuous recording paper delivered from a paper roll according to the related art is described in JP-A-2001-278518, for example. The printer described in JP-A-2001-278518 has a conveyance mechanism that conveys recording paper delivered from a paper roll, a tension adjustment roller disposed on the upstream side in the conveyance direction of the recording paper from the conveyance mechanism, a motor that drives the tension adjustment roller, and a control unit that controls driving the conveyance mechanism and the motor. The control unit uses PID control to control the motor to maintain constant tension (back tension) on the recording paper between the conveyance mechanism and the roller when conveying the recording paper by the conveyance mechanism. The control unit also uses PID control to control the motor to maintain constant tension on the recording paper between the conveyance mechanism and the roller when conveyance of the recording paper by the conveyance mechanism is stopped.
If the medium is pulled in the opposite of the conveyance direction due to the inertia of the paper roll, for example, when starting to convey the media (recording paper) delivered from the roll (paper roll), the tension on the media increases. Because this increase in tension affects the conveyance precision of the media, the media is delivered from the paper roll or the media is rewound onto the roll in order to keep the tension on the medium at a specific tension level. If the tension on the medium also remains constant after media conveyance stops as described in JP-A-2001-278518, there is no need to deliver or rewind the medium at the start of media conveyance, the printing operation can therefore start quickly, and the throughput of the printing process improves.
However, if PID control of the motor continues to maintain constant tension on the medium even after media conveyance stops, the motor is driven in reaction to change in the tension on the medium even when the medium sags slightly. With PID control, however, the change in tension is time integrated and reflected in how much the motor is controlled even when there is a slight variation in tension, and the motor continues being driven even after media conveyance has stopped. Preventing the motor from heating even after media conveyance has stopped can therefore be difficult.